In the telecommunications industry, voice and data signals are often transmitted over long distances along groups of closely spaced transmission lines. In order to maintain flexibility as equipment is added or replaced in a telecommunications system, it is important to have connection stations at one or more locations where connections to a large number of pieces of equipment can be made.
Electromagnetic radiation and interference are generated between adjacent transmission lines, particularly where the lines are spaced closely together. The radiation can cause electromagnetic coupling between adjacent transmission lines which can adversely affect the information being transmitted. For example, the radiation can generate “crosstalk” in the transmission lines. The effects of crosstalk can be reduced by transmitting the information over twisted pairs, or over wires that are encased in a conductive sheath, for example. Such techniques may be useful for reducing crosstalk over the extent of the transmission lines. However, the transmission lines are ultimately terminated at connector blocks located at connection stations. The conductors in the connector blocks are closely spaced apart and, as such, there is a tendency for crosstalk. However, it may not be practical to use the described techniques for reducing crosstalk in connector blocks.
The problem of crosstalk may not be particularly severe at low frequencies of less than 16 megahertz (MHz), for example. However, there is a demand for transmission at much higher frequencies, such as 100 MHz and more, and, at those frequencies, radiation is higher and there is a greater tendency for crosstalk.
A screening device for the insulation displacement contacts (IDCs) of a connector block is described in U.S. Pat. No. 5,160,273. Here the problem of crosstalk between adjacent groups of electric connectors, such as IDCs, is solved by inserting electrically conductive screening plates between adjacent pairs of IDCs. The plates are inserted into slots which extend transversely to the longitudinal direction of the plastic body of the connector block and contact a base rail situated in the longitudinal direction of the inside of the plastic body of the connector block. A disadvantage of this arrangement is that, when fitting the component into the plastic body, it is first necessary to fit the base rail, which has contact tongues for contacting the individual screening plates, and that it is subsequently necessary to push the individual screening plates into the connector block. Consequently, the complexity of assembly is relatively high.
Notwithstanding the fact that the screening taught by U.S. Pat. No. 5,160,273 may reduce crosstalk in connector blocks, it may still allow unacceptably high levels of crosstalk at high frequency data transmission rates.
It is generally desirable to overcome or ameliorate one or more of the above mentioned difficulties, or at least provide a useful alternative.